1. Field
The aspects of the disclosed embodiments relate to a method of pulping wood or non-wood, and papermaking wherein the amounts of effluents generated by these processes are decreased, and more specifically to a process of chemical pulping and papermaking providing a processing step contributing especially to an improvement in chemical consumption, washing efficiency and dewatering of pulp, yielding enhanced final paper product properties and higher productivity.
2. Brief Description of Related Developments
Pulp washing and dewatering of the fibers in pulping and papermaking processes creates a substantial amounts of effluents, consumption of bleaching chemicals, increases the amount of water and energy in these processes.
Pulping processes today commonly include semi chemical, mechanical and chemical pulping processes, which are used for pulping hardwood, softwood and non-wood raw materials. Various additives are used in order to improve economy in chemical consumption and washing of the pulp as well as the economy of the pulp production.
Fibers thereby obtained are generally used in the papermaking processes such as neutral, acidic and alkaline. Various additives are used in order to improve the quality of the paper obtained as well as the economy of the papermaking.
There are patents CA 1066697, U.S. Pat. No. 4,869,783 and Fl 68680 which are teaching some beneficial effects of the mechanical defibration of biomass particles on cooking yield or cooking time, while maintaining paper technical properties of the pulp.
Publication CA 1066697 discloses that rupture and damage to fiber cell caused by processes taught by prior art publications can be avoided by impregnating shredded chips of 2 by 2 mm first with alkali solution of weaker chemical activity whereby inhibiting the delignification of the particles and then with alkali solution of stronger chemical activity. The temperature has to be increased slowly in order to avoid delignification and cell wall damages. This document explicitly teaches that intact lignin layer is necessary for protection against mechanical defibration. The fine size of the chips is also considered as essential.
Similar effect is taught by U.S. Pat. No. 4,869,783 by preheating with steam the biomaterial pieces before separation of the fibers by defibering and leaving the chips partially defibered. It does not teach impregnation prior to defibering. Partially defibered chips and damaged fibers before cooking have fiber middle lamella, which allows in the cooking phase, chemicals to act directly on the middle lamella without passing through the fiber wall as illustrated in FIG. 5. However the method of this disclosure also fails for the same reason as CA 1066697 to improve drainage time or significantly affect the density of the pulp sheet at the same yield or kappa number level. This is evident from the examples 1 to 5 of the publication U.S. Pat. No. 4,869,783.
The publication Fl 68680 teaches how resins can be removed after cooking from washed brown stock pulp pressing the pulp by rotating screws in alkali solution.
Publication U.S. Pat. No. 6,458,245 presents a process for defibering impregnated and preheated wood chips in order to produce chemithermomechanical pulp. The objective of these processes is to remove fibers as intact as possible from the chip matrix and continue with cooking or bleaching process. In this way as described in cited publications above the cell wall will remain intact or will be partially removed/damaged. The general strategy applied in these solutions is to expose and subsequently remove the middle lamella to prompt and contribute to fibre separation.
In the prior art, there are also several patents regarding pulping processes and improving washing and decrease of water usage and chemical consumption in the pulping processes especially in Kraft pulping process.
From the prior art it is known a process for enhancing pulp washing efficiency by decreasing the tendency of lignin to remain with the pulp fraction during washing. In this method, anionic surfactants are added within the washing or pulping operation to enhance the removal of lignin.
It is also known to those in the art, that bleaching of pulp by hydrogen peroxide and in particular to a method of treating pulping liquors by preventing or reducing the breakdown of peroxide by catalase. By consuming hydrogen peroxide, catalase can lower bleaching efficiency and decrease brightness levels of the finished paper, thereby increasing chemical consumption.
There are several patents regarding enhanced dewatering in papermaking and decrease of water usage in papermaking. There are also several patents related to the surface evenness improvements and bulk improvements. There are also patents to improve porosity of the paper especially e.g. for filter papers. There are also patents for improving pulp optical properties and absorbance for e.g. of fluff or softness (bulk) of tissue pulp.
From prior art it is known a method of dewatering aqueous cellulosic pulp slurry which method comprises adding to aqueous slurry of washed cellulosic pulp an effective dewatering amount of a mixture of one or more nonionic surfactants and one or more anionic surfactants.
Experts in the art are also familiar with the general field of fluid absorbing products and, more particularly, to a highly absorbent and flexible pulp sheet. More specifically, the flexible and absorbent sheet comprises densified and mechanically worked cellulosic pulp fluff material which has a high structural integrity and provides a soft, thin and flexible fluid absorbent core having good wicking characteristics, well-suited for use in disposable absorbent products such as sanitary napkins, wound dressings, bandages, incontinence pads, disposable diapers and the like. A method of pre-paring such highly absorbent and flexible cellulosic pulp fluff sheet and its method of use in disposable absorbent products is also provided.
It has been also known from earlier work that by decreasing the amount of hemicelluloses in the fibers the washing and dewatering of the pulp can be enhanced. This can be done for e.g. by cooking the pulp to lower kappa numbers. However this will decrease the cooking yield and therefore increase wood consumption and it is not economically feasible. The use of chemical additives for enhancing the dewatering or washing is also known from the art and will not lead to substantial increase in the dewatering efficiency and will only add an additive to the system which remains therein circulating.
The use of enzymes in bleaching does not usually decrease the cost of bleaching and the amount of effluent generated which is also known from prior art.
From prior art it is also known, that the structure of cellulosic fiber inhibits processing ethanol. Pretreatment is one of the most important operations for practical cellulose conversion processes, and is a key technical barrier to using cellulosic feedstocks for bioconversion. Pretreatment is required to alter the structure of cellulosic biomass to make cellulose more accessible to the enzymes that convert the carbohydrate polymers into fermentable sugars. An effective pretreatment will disrupt the physical and chemical barriers posed by cell walls, as well as cellulose crystallinity, so that hydrolytic enzymes can access the biomass macrostructure. The low accessibility of enzymes into untreated lignocellulosic matrices is the key hurdle to the commercial success of converting cellulosic biomass to biofuel.
Those who are experts in the art also know that, cellulose is characterized by insolubility, in particular in customary solvents of organic chemistry. In general, N-methylmorpholine N-oxide, anhydrous hydrazine, binary mixtures, such as methylamine/dimethyl sulfoxide, or ternary mixtures, such as ethylenediamine/SO2/dimethyl sulfoxide, are nowadays used as solvents. However, it is also possible to use salt-comprising systems such as LiCl/dimethylacetamide, LiCl/N-methylpyrrolidone, potassium thiocyanate/dimethyl sulfoxide, etc. Said application discloses a process for the degradation of cellulose, which comprises dissolving cellulose in an ionic liquid, and treating this solution at elevated temperatures, if appropriate in the presence of water.
Even though many solutions have been suggested, there still remains a need for an environmentally friendly pulping and papermaking process applicable to variety of plants and mills, both planned and existing.